Extra-renal vascular renin had not been clearly demonstrated partly because the levels are very low. Since acid proteases (AP), active at this pH6, may both generate Angiotensin I (AI) and destroy apparent RLA, protease inhibitors and affinity chromatography were used. In aortas collected from animal 24 hours after nephrectomy and 18 hours after hemorrhage no detectable RLA was present. No RLA was found in cerebral microvessels nor was it present in the aortas of spontaneously hypertensive rats collected 24 hrs after bilateral nephrectomy. Anti-renin antibody completely inhibited rat PRA and vascular RLA. Vascular RLA appears to arise from the plasma, and extravenal vessels do not appear to be a separate source of renin.